The present invention generally relates to a braking force controlling apparatus, and more particularly to a braking force controlling apparatus which changes a magnitude of a braking force produced in response to a braking operation based on a speed of the braking operation.
As disclosed in Japanese Laid-Open Patent Application No. 4-121260, there is known a braking force controlling apparatus which generates an increased braking force larger than a braking force during a normal control, when it is detected that an emergency braking operation is performed on an automotive vehicle. The conventional apparatus of the above publication is provided with a brake booster which generates a boosted pressure in response to a braking operation force Fp on a brake pedal of the vehicle, or the boosted pressure being equal to the braking operation force Fp multiplied by a given magnification factor. The boosted pressure is delivered from the brake booster to a master cylinder. The master cylinder generates a master cylinder pressure Pmc in response to the boosted pressure delivered from the brake booster, and the master cylinder pressure Pmc is proportional to the braking operation force Fp.
Further, the conventional apparatus of the above publication is provided with a high-pressure source having a pump which generates a brake-assisting pressure. The high-pressure source generates a brake-assisting pressure in accordance with a drive signal supplied by a control circuit. When a speed of the braking operation of the brake pedal exceeds a reference speed, it is determined that an emergency braking operation is performed by a vehicle operator, and the control circuit supplies a drive signal to the high-pressure source, the drive signal requesting a maximum brake-assisting pressure to be generated by the high-pressure source. Both the brake-assisting pressure generated by the high-pressure source and the master cylinder pressure Pmc generated by the master cylinder are supplied to a switching valve, and the switching valve delivers a larger one of the brake-assisting pressure and the master cylinder Pmc to wheel cylinders of the vehicle.
In the conventional apparatus of the above publication, when the speed of the braking operation is below the reference speed, the master cylinder pressure Pmc, which is proportional to the braking operation force Fp, is supplied to the wheel cylinders. Hereinafter, the control that is performed to generate the braking force by the braking operation under such a condition will be called a normal control. On the other hand, when the speed of the braking operation is above the reference speed, the brake-assisting pressure, which is generated by the high-pressure source, is supplied to the wheel cylinders. Hereinafter, the control that is performed to generate an increased braking force larger than the braking force generated during the normal control, under such a condition, will be called a brake-assisting control.
In the conventional apparatus of the above publication, when the braking operation of the brake pedal is performed at a normal speed, the braking force is controlled to the magnitude that is proportional to the braking operation force Fp, and, when the emergency braking operation of the brake pedal is performed, the braking force is quickly increased to be larger than the braking force during the normal control.
When a condition that requires the emergency braking operation is avoided, it is necessary to terminate the brake-assisting control and restart the normal control. The vehicle operator releases the braking operation force on the brake pedal after the condition requiring the emergency braking is avoided. If such a decrease of the braking operation force on the brake pedal is detected, it is possible to determine the time of termination of the brake-assisting control based on the detected braking operation force decrease.
However, according to experiments performed by the inventors of the present invention, it is concluded that beginners who are less experienced in vehicle operation tend to unintentionally release the brake pedal during the emergency braking operation. In the conventional apparatus of the above publication, when the decrease of the braking operation force on the brake pedal is detected, the brake-assisting control is automatically terminated even if a beginner unintentionally releases the brake pedal.
Therefore, when the beginner unintentionally releases the braking operation force on the brake pedal during the emergency braking operation, the conventional apparatus of the above publication automatically terminates the brake-assisting control and restarts the normal control based on the detected braking operation force change. However, the condition requiring the emergency braking still exists when the brake-assisting control is terminated. In such a case, the termination of the braking-assisting control is too early to ensure a vehicle running stability. Hence, the capability of the conventional apparatus of the above publication is inadequate to effectively achieve the function of the brake-assisting control.
An object of the present invention is to provide an improved braking force controlling apparatus in which the above-described problems are eliminated.
Another, more specific object of the present invention is to provide a braking force controlling apparatus which safely maintains the brake-assisting control even if a beginner unintentionally releases the braking operation force on the brake pedal during the emergency braking operation.
The above-mentioned objects of the present invention are achieved by a braking force controlling apparatus which selectively performs one of a normal control to generate a braking force by a braking operation and a brake-assisting control to generate an increased braking force larger than the braking force generated during the normal control, the apparatus comprising: an operation quantity detection means which detects a quantity of a braking operation of a brake pedal; a maximum operation quantity storage means which stores a maximum quantity of the braking operation during the braking operation of the brake pedal; and a brake-assisting control termination judgment means which determines whether the brake-assisting control should be terminated based on the braking operation quantity detected by the operation quantity detection means and the maximum quantity stored by the maximum operation quantity storage means.
In the braking force controlling apparatus of the present invention, the time of termination of the brake-assisting control is determined based on the braking operation quantity detected by the operation quantity detection means and the maximum quantity stored by the maximum operation quantity storage means.
When the emergency braking is required, an experienced vehicle operator intentionally maintains the braking operation force on the brake pedal. After the condition requiring the emergency braking is avoided, the vehicle operator intentionally releases the braking operation force on the brake pedal. However, the beginner tends to unintentionally release the brake pedal during the emergency braking operation, which causes a decrease of the braking operation force on the brake pedal.
Generally, a decrease of the quantity of the braking operation of the brake pedal by an unintentional operation of the beginner is smaller than a decrease of the quantity of the braking operation by an intentional operation of the experienced vehicle operator. It is possible to determine whether the braking operation of the brake pedal is performed intentionally or not, by correctly detecting the decrease of the quantity of the braking operation.
Accordingly, it is possible for the braking force controlling apparatus of the present invention to maintain the brake-assisting control when the decrease of the quantity of the braking operation is determined as being not caused by the intentional operation, and to terminate the brake-assisting control when the decrease of the quantity of the braking operation is determined as being caused by the intentional operation.
In addition, the quantity of the braking operation of the brake pedal during the emergency braking operation may differ according to the individual vehicle operators. In the braking force controlling apparatus of the present invention, a maximum quantity of the braking operation during the braking operation is stored by the maximum operation quantity storage means. The determination as to whether the brake-assisting control should be terminated is made based on the maximum quantity stored by the maximum operation quantity storage means and the braking operation quantity detected by the operation quantity detection means. It is possible to determine the time of the termination of the brake-assisting control with accuracy by eliminating the differences of the braking operation quantity according to the individual vehicle operators.
In a preferred embodiment of the present invention, the braking force controlling apparatus may be constructed such that the brake-assisting control termination judgment means terminates the brake-assisting control when the braking operation quantity is smaller than a difference between the maximum quantity and a predetermined decrease quantity. Further, in another preferred embodiment of the present invention, the braking force controlling apparatus may be constructed such that the brake-assisting control termination judgment means terminates the brake-assisting control when the braking operation quantity is smaller than a product of the maximum quantity and a decrease ratio.
In these embodiments of the present invention, it is possible to determine the time of the termination of the brake-assisting control with an increased accuracy by setting the decrease quantity or the decrease ratio at an appropriate value.
In a preferred embodiment of the present invention, the braking force controlling apparatus may be constructed such that the brake-assisting control termination judgment means determines whether a brake releasing operation during the brake-assisting control is an intentional operation based on the braking operation quantity detected by the operation quantity detection means and the maximum quantity stored by the maximum operation quantity storage means, wherein, when the brake releasing operation is determined as being not an intentional operation, the brake-assisting control termination judgment means maintains the brake-assisting control.
The above-mentioned objects of the present invention are achieved by a braking force controlling apparatus which selectively performs one of a normal control to generate a braking force by a braking operation and a brake-assisting control to generate an increased braking force larger than the braking force generated during the normal control, the apparatus comprising: an operation quantity detection means which detects a quantity of a braking operation of a brake pedal; a maximum operation quantity storage means which stores a maximum quantity of the braking operation during the braking operation of the brake pedal; and a brake-assisting control continuation judgment means which determines whether a brake releasing operation during the brake-assisting control is an intentional operation based on the braking operation quantity detected by the operation quantity detection means and the maximum quantity stored by the maximum operation quantity storage means, wherein, when the brake releasing operation is determined as being not an intentional operation, the brake-assisting control continuation judgment means maintains the brake-assisting control.
In the braking force controlling apparatus of the present invention, the brake-assisting control continuation judgment means determines whether a brake releasing operation during the brake-assisting control is an intentional operation. When the brake releasing operation is determined as being not an intentional operation, the brake-assisting control continuation judgment means maintains the brake-assisting control. Hence, when the emergency braking is required, it is possible for the braking force controlling apparatus of the present invention to quickly increase the braking force to be larger than the level during the normal control by maintaining the brake-assisting control.
In the braking force controlling apparatus of the present invention, the brake-assisting control continuation judgment means makes the determination as to whether the brake releasing operation during the brake-assisting control is an intentional operation, based on the braking operation quantity detected by the operation quantity detection means and the maximum quantity stored by the maximum operation quantity storage means. When the brake releasing operation is determined as being an intentional operation, the brake-assisting control continuation judgment means terminates the brake-assisting control. However, when the brake releasing operation is determined as being not an intentional operation, the brake-assisting control continuation judgment means maintains the brake-assisting control. Hence, the braking force controlling apparatus of the present invention is effective in maintaining the brake-assisting control even if a beginner unintentionally releases the braking operation force on the brake pedal during the emergency braking operation.